If you are in a hurry==>Contour lines

  1. Select button: Contour lines
  2. Define region holding data points
  3. Select method: Cubic
  4. Create new layer: Cubic
  5. State height levels
  6. Calculate
  7. Eventually improve curves (optional)
  8. Add Tags
  9. Select colour, type and line width (Optional)
  10. Close
  11. Export

See a video of the whole process